In the conventional manner of making heat exchange panels, pair of superposed metal sheets are welded together at different places to form a desired pattern of passageways. Spot welds may be used to form a flooded type heat exchange panel, while seam welds may be used to form a serpentine passage way in the panel. Either type of weld may be made in one or both of the metal sheet by conventional welding methods, such as the plug welding or the resistance welding method, in which the metal sheets are pressed together with two electrodes, or by the inflation method, in which the pattern is painted on one or both of the sheets with a nonbonding or weld-preventing composition, usually consisting of a mixture of graphite in water glass, and the two sheets are then welded together by the conventional hot rolling process. The latter method is described in U.S. Pat. Nos. 2,680,002, issued Sept. 28, 1954 and 2,982,013, issued May 2, 1961. Another example or the prior art is described in U.S. Pat. No. 1,709,865, issued Aug. 23, 1929. After the sheets have been welded together with the desired pattern outlined on one or both of the sheets, the double-surfaced blank is placed on a stretcher table with the opposing welded edges held in clamped position under slight tension. A high pressure fluid is then injected through an opening formed between the two sheets and a high pressure tube welded thereto to distend the non-welded area ot the blank and thus form the selected pattern of passageways for the heat exchange fluid to be supplied through openings subsequently formed in the blank by means of special fittings and couplings connected to an inlet duc and an outlet duct, respectively, in the completed article.
In the spot-welded version, or flooded type, of heat exchange panel, the distended area of the blank assumes a "pillowed" effect. The degree of fluid pressure required to distend the non-joined area of the blank and to cause the "pillowed" effect, will, of course, vary with gauge and composition of the metal used. As an example, the heat exchange panel manufactured by Dean Products, Inc., identified as "Panelcoil"900 series, is made of 12-18 gauge stainless steel and requires an inflation pressure if 300 PSIG to 400 PSIG to obtain a "pillow" height on both sides of the facing sheets averaging between 0.120" to 0.150" and designed for operating pressures between 50 PSIG and 500 PSIG. In heat exchange panels where only one of the superposed sheets is embossed, the non-embossed sheet obviously must be heavier gauge, in order to withstand the aforementioned inflation pressure.
Conventionally, after the sheet metal blank has been inflated or "pillowed", the metal in one or both of the sheets is distorted or pried apart to form an inlet and an outlet for the heat exchange fluid to be circulated through the heat exchange panel, and the inlet opening for the inflation fluid is sealed. These inlets and outlets must be sufficiently large to accommodate the pipe fittings for the source of heat exchange fluid to supply this fluid in sufficient volume to flood the passageways in the heat exchange panel. To ensure complete flooding of the passageways, the outlet opening preferably is of smaller dimensions than the inlet opening, to create the required operating pressures. These operating presures may vary between 50 PSIG and 1000 PSIG, depending on the type of metal used and the thickness thereof, which pressures may cause weakening or distortion of the passageways, or even cause separation between the two facing sheets,
Heretofore, it was not thought possible to inject the high pressure fluid through the same fittings or couplings that are used for circulating the heat exchange fluid, because the high stress created by the large volume of high pressure inflation fluid would cause the welds to "blow" . Thus, according to U.S. Pat. No. 1,709,865, supra, the normal inlet fitting for the heat exchange fluid is replaced by a separate pipe for introducing the inflation fluid, while the outlet opening for the heat exchange fluid if plugged. According to U.S. Pat. No. 2,690,002, supra, a hole is drilled into the passageway for the heat exchange fluid after the expansion process is completed, which hole is fitted with a tube to allow circulation of heat exchange fluid through the heat exchange panel. See also U.S. Pat. No. 3,512,239, which suggests the formation of another opening after the inflation process has been completed, which opening, along with the opening for introducing the hydrostatic pressure between the plates, provides for flow of heat exchange fluid through the passageways.
The applicants have now made the unobvious discovery that by using couplings substantially as disclosed in U. S. Pat. Nos. 3,126,215 and 3,141,500, granted to the common assignee of this application, heat exchange panels can be produced economically without the use of a separate fitting for the inflation fluid.
Other examples of prior are are shown in U.S. Pat. Nos 3,512,239 and 3,736,783 .